High voltage direct current transmission for transmitting energy on a large scale is regaining attention for various reasons. The re-advent of DC grids is strongly linked to a different concept of how to drive the power into the DC grid. Future DC grids may be controlled by a voltage controlled source, also known as voltage source converters (VSC). In such grids, a fault current may rise very fast in case of a short circuit and as a result may burden system reliability.
In the event of a short circuit in a known AC grid, an interrupt concept may benefit from the alternating properties of the AC current in the grid. When opening an associated circuit breaker in the AC current path, an electric arc may electrically connect such circuit breaker electrodes and may continue to allow an electric arc current to cross the circuit breaker. However, due to the nature of the AC driving source such ongoing electric arc current in the AC current path may oscillate, too, and inherently may show zero current crossings. A zero crossing in current is desired for extinguishing the electric arc and for stopping the current flow across the circuit breaker completely.
In DC grids, however, no such zero current crossing occurs as a by-product of the driving source, but a current zero in the DC current path is desired to be generated by other means when or after the circuit breaker is effected to its open state. In one approach, a current zero is caused by injecting an oscillating counter-current into the DC current path. Such oscillating counter-current may counteract the electric arc current and may finally cause at least a temporary current zero to appear in the DC current path which in turn may be used for extinguishing the electric arc at the circuit breaker and make the current flow in the DC current path stop. A means for evoking an oscillating counter-current is a resonance circuit arranged in parallel to the circuit breaker, in which the circuit breaker is more generally denoted as a switchable element or switching element below. However, in the event of connecting the resonance circuit in parallel to the switching element, a certain rise time needs to lapse before the oscillating counter-current reaches a magnitude sufficient to counterbalance the electric arc current across the switching element. Such rise time may depend on the voltage drop across the electric arc and on the capacitance present in the resonance circuit. While a high capacitance value is preferred in view of short oscillation rise times, associated capacitors are cost intensive.
In WO 2009/149749 A1, a device for breaking DC currents exceeding 2500 A is disclosed. This device includes a resonance circuit connected in parallel with an interrupter. A surge arrester is connected in parallel with the resonance circuit. The resonance circuit has a series connection of a capacitor and an inductance. The relationship of the capacitance in μF to the inductance in μH of the resonance circuit is >=1.